Eighteen patients were identified in whom ultrasound (US) of the kidney demonstrated a hyperechoic medulla. Diagnoses in the patients included gout in seven; Sjögren syndrome in two; medullary sponge kidney in two; primary aldosteronism in two; and Lesch-Nyhan syndrome, hyperparathyroidism, glycogen storage disease type XI, Wilson disease, and pseudo-Bartter syndrome in one each. The pathogenesis of the echogenicity was evaluated by comparing the findings from computed tomography and conventional radiography. It appears that a hyperechoic medulla is caused by hyperuricemia, medullary nephrocalcinosis, or hypokalemia. US is considered to be useful in evaluating renal involvement in patients with these diseases.